Question: Simplify the following expression: $y = \dfrac{t}{9} - \dfrac{2t}{5}$
Explanation: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $9$ and $5$ $\lcm(9, 5) = 45$ $ y = \dfrac{5}{5} \cdot \dfrac{t}{9} - \dfrac{9}{9} \cdot \dfrac{2t}{5} $ $y = \dfrac{5t}{45} - \dfrac{18t}{45}$ $y = \dfrac{5t -18t}{45}$ $y = \dfrac{-13t}{45}$